Gregory Lynn Shrader, 55, of Jay, Okla., was charged with willfully making a threat after investigators discovered he tried to send an improvised explosive device through the mail last April to Arpaio's headquarters in Phoenix from a post office box in Flagstaff, records show.

Postal workers in Flagstaff noticed the suspicious package by its excessive stamp postage and typewritten addressee label, according to a complaint filed Thursday in U.S. District Court in Arizona.

While inspecting the cardboard box, postal inspection agents observed a silver grain-like substance spilling from one of the seams. After extensive screening, it was determined to be an explosive smokeless powder, according to court documents.

The Flagstaff Police Department's Explosive Ordinance Disposal team was called to the scene, where they viewed the contents of the package with a robot equipped with an X-ray camera. The contents showed wires, batteries, a detonation mechanism booby-trapped to the lid of the box, as well as the smokeless powder and an unknown bottled substance.

The device was disabled by law enforcement, who then began to trace where it came from and who sent it.

The name on the return address was linked to a man in California who denied sending or having knowledge of the package. He claimed his former business partner, Gregory Shrader, was attempting to frame him, and that it wasn't the first time, according to court documents.

Based on the man's statements, law enforcement officials began investigating whether Shrader was a person of interest by documenting his bank activity and tracing him through security footage collected between stops on his drive from Oklahoma to Flagstaff, according to court documents.

After compiling photographic evidence and witness statement, a search warrant was served at Shrader's residence in Jay, a small town with a population of 2,400 people in the northeast corner of Oklahoma, near the Arkansas border.

It was unclear Tuesday if Shrader had lawyer.

"It's good to have the guy off the street," Arpaio said Tuesday. "I'm grateful that the feds did a good job. The postal service and the FBI have been working on this for almost a year, and they got the guy."

Arpaio, the self-proclaimed "toughest sheriff in America," has had a security detail for years and said he regularly receives threats including "at least 12 in the last year."

The 81-year-old Arpaio has been sheriff of Arizona's Maricopa County since 1993 and is known nationally for his strict treatment of jail inmates and cracking down on illegal immigration.

But Arpaio said the explosive package case was especially troubling "because it could have caused havoc if it was opened up and been dangerous for me and people around me."